If they were still handing out Shift_ titles I would recommend yours be Shift_Professor. Please tell me you didn't just copy and paste that from somewhere.It is true that N has a lower molecular weight than O but both molecules exist in the diatomic state, N2 and O2 with molecular weights of 28 and 32 , respectively. Based on this information it would appear at first look that O2 is the larger molecule because it is mistakenly assumed that molecular weight correlates with molecule size.
The diatomic state of the two molecules, instead of existing as spheres, exist as bean shapes where the molecules are longer than they are wide. The reason that O2 behaves as a smaller molecule than N2, despite its larger molecular weight, deals with its atomic electron cloud. The O2 electron cloud, due to the higher number of protons in its nucleus, is pulled tighter and denser by the greater charge of the O2 nucleus, much like cinching a belt across the "waist" of the molecule. The N2 molecule wears a larger belt size due to it weaker nucleus charge and behaves as a larger molecule than O2 with respect to gas permeation.
Although N2 has an apparent effective larger size, despite its smaller molecular weight, the size difference between the two is not worth a bucket of warm spit. The primary advantage of N2 is that it is not O2. Nitrogen is considered inert where oxygen is very reactive, think oxidation. The other advantage, as stated above, is that nitrogen is delivered to the tire in a dry state without water.